IGCSE Biology Paper-4: Specimen Questions with Answers 148 - 148 of 279

Question 148

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Describe how blood is transported from the vena cava to the lungs. You may use the letters on Fig. in your description.

Explanation

Physiology of heart: The heart pumps blood to all parts of the body. The deoxygenated blood is drained into right auricle through superior and inferior venae cavae and coronary sinus whereas the pulmonary veins carry oxygenated blood from lungs to the left auricle. This is called as Auricular circulation. About 70 % of the auricular blood passes into the ventricles during diastole. This phase is called diastasis. The rest of 30 % of blood passes into the ventricles due to auricular systole (contraction) . In this way, blood reaches the ventricles and is called ventricular filling. During ventricular systole (which starts first in left ventricle than in right ventricle) , the pressure increases in the ventricles, thus, forcing the oxygenated blood from left ventricle into systemic aorta and deoxygenated blood from right ventricle into pulmonary aorta. The systemic arch distributes the oxygenated blood to all the body parts except lungs while pulmonary aorta carries the deoxygenated blood to lungs for oxygenation.